Development of a Grounding System Circuit Model for Transient Analysis Based on Frequency Spectrum of Lightning Current

Ground Potential Rise (GPR) generated by lightning strikes can result in hazardous voltages near hit structure. In this context, several models have been developed in theliterature to accurately represent the grounding systems of Lightning Protection Systems (LPS), taking into account more realistic soil characteristics. Utilizing an appropriate model that generates approximate results for diverse LPS geometries, a direct time-domain assessment of GPR can provide an efficient and fast estimation. This is particularly valuable in the development of practical resources for LPS projects, encompassing the analysis of physical installation aspects and the evaluation of risks linked to concealed grid ruptures or disconnections, and potential enhancements through alterations in electrode geometries and positioning. The influence of frequency-dependent soil parameters (FDSP) is crucial and cannot be overlooked when attempting to realistically express GPR, especially for higher soil resistivity. This article introduces an method known as the Filtered Frequency Spectrum Method (FFSM) to efficiently evaluate GPR while considering FDSP. The simulations utilize a simplified grounding system circuit model incorporated into ATP-EMTP software. The frequency spectrum of the lightning current is obtained through a Fast Fourier Transform (FFT); the spectrum is then segmented into bands using filters to select a representative frequency where the FDSP are evaluated. For each band, a circuit model is constructed using Transmission Line Modeling. The resulting GPR is calculated as the sum of the filtered results. Results demonstrated that the GPR calculated using the FFSM presents a good agreement compared with those assessed with traditional recursive methods. The performance of the FFSM is better for soils of low and moderate resistivity and does not require the traditional frequency-to-time conversion tools.